The recycling of produced water and oilfield waste from unconven- tional oil and gas development (UD) has recently garnered significant attention given the scarcity of fresh water in many shale energy basins across the United States. For example, in 2011, 18.5 billion liters of water was used to stimulate unconventional production wells in Texas, which accounted for b1% of the state’s water usage (Scanlon et al., 2014; Shaffer et al., 2013). However, these volumes tend to be highly localized, which can lead to ground water depletion, especially in arid and semiarid regions.
In addition to the requirement for large amounts of water, UD, as with conventional oil and gas development, also generates a tremen- dous amount of wastewater, commonly referred to as produced water (PW). This waste stream begins with flowback water (FBW: initial frac- turing fluid returning to the surface), then transitions into produced water (a combination of formation water and fracturing fluid that is comingled with the oil and natural gas), which continues to be pro- duced over the lifetime of a UD well (Liden et al., 2017). In 2012, oil and gas development in the United States generated an estimated 21.2 billion barrels (bbl) of produced water (58 million bbl/day), with Texas accounting for 35% of the national PW volume with N7.4 billion bbl (Veil, 2015).
Due to economics and convenience, subsurface injection has been the primary method of PW management in the United States, with up to 98% of PW being reinjected (Oetjen et al., 2017). Reinjection into a productive petroliferous formation can aide in oil recovery, whereas in- jection in a non-production formation can accomplish waste sequestra- tion. However, the disposal of PW into salt-water disposal (SWD) wells has been linked to induced seismicity in some areas where the number of earthquakes correlates with the volume of PW being injected (Hornbach et al., 2016; Hornbach et al., 2015; van der Elst et al., 2015). It is thought that these anthropogenic events are the result of in- creased fluid pressure on already stressed faults, triggering preexisting faults to slip (Walsh and Zoback, 2015). As such, in addition to the in- herent value of reducing the reliance on fresh water resources, particu- larly where water scarcity is an issue, the increased frequency of these UD-related earthquakes has provided motivation to reevaluate the via- bility of PW recycling for the sake of environmental stewardship.